• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.229-235
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• 2018

In this study, recycled aggregate and natural aggregate were mixed in advance using an aggregate mixing facility that was developed to improve the quality of recycled aggregate concrete. Then the mixed aggregate was applied and concrete characteristics before and after a mix were considered. Based on the findings extracted, this study aimed to suggest a new direction for quality stabilization and application activation of recycled aggregate. The test results of change rates of mortars and coarse aggregates in fresh concrete mixed by a concrete mixer, before and after mixing aggregates showed that the variations of the mortars and coarse aggregates in the concrete mixed with the aggregates beforehand were decreased than those in the concrete before mixing them. The variation of compressive strength and the mean compressive strength at the ages of 3 and 7 days showed similar results before and after the aggregates were mixed, and the strength at the age of 28 days before and after mixing them showed larger deviation than that at the ages of 3 and 7 days. The use of the mixed aggregates after mixing aggregates beforehand reduced the variation in strength and is believed that it is advantageous for long-age strength development. The above results show that the variations of coarse aggregates and compressive strength in the concrete using the mixed aggregates produced by mixing recycled aggregates and natural aggregates beforehand are reduced so it will be possible to produce the homogeneous concrete by mixing aggregates beforehand.

• Advances in concrete construction
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• v.3 no.1
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• pp.55-69
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• 2015

Tailing Material (TM) and Fly Ash (FA) are obtained as waste products from the mining and thermal industries. Studies were carried out to explore the possibility of utilizing TM as a part replacement to fine aggregate and FA as a part replacement to cement, in concrete mixes. The effect of replacing fine aggregate by TM and cement by FA on the standard sized specimen for compressive strength, split tensile strength, and flexural strengths are evaluated in this study. The concrete mix of M40 grade was adopted with water cement ratio equal to 0.40. Concrete mix with 35% TM and 65% natural sand (TM35/S65) has shown superior performance in strength as against (TM0/S100, TM30/S70, TM40/S60, TM50/S50, and TM60/S40). For this composition, studies were performed to propose the optimal replacement of Ordinary Portland Cement (OPC) by FA (Replacement levels studied were 20%, 30%, 40% and 50%). Replacement level of 20% OPC by FA, has shown about 0-5% more compressive strength as against the control mix, for both 28 day and 56 days of water curing. Interestingly results of split tensile and flexural strengths for 20% OPC replaced by FA, have shown strengths equal to that of no replacement (control mix).

• Journal of the Korea Concrete Institute
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• v.25 no.3
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• pp.347-354
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• 2013

Recently, crushed fine aggregates are being widely used due to the shortage of natural sand. In Korea, the amount of fine particles under 0.08 mm contained in crushed fine aggregates is restricted to be less than 7%, which is similar to the regulations of ASTM but is still very strict compared to the regulations of the other nations. In addition, the crushed aggregates already have in them about 20% of fine particles under 0.08 mm which occurs while they are crushed. The fine particles are not easy to wash out, and also to maximize the use of resources it is deemed necessary to review the possibility of enhancing the limit of the amount of fine particles. Therefore, this study conducted experiments to analyze the characteristics of fine particles under 0.08mm and their influence on the properties of concrete. Experiments using silt and cohesive soil were also done for comparison. In the experiments on fine particles, the methylene blue value was more in the soil dust contained in silt and cohesive soil than in the stone powder contained in crushed fine aggregates. Also, the methylene blue value had a close correlation with packing density and liquid & plastic limit. In the experiments done with concrete, the quantity of high range water reducing agent demanded to obtain the same slump increased as the fine particle substitution rate heightened. However, in the experiment which used stone powder testing the compressive strength and tensile strength of concrete in the same water-cement ratio, there was little change in strength with less than 20% addition of fine particles among the fine aggregates, and no meaningful difference in the amount of drying shrinkage of concrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.105-115
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• 2010

In this study, as one of solutions associated with the shortage of treatment area of industrial waste and the containment of its harmful components, the bottom ash which is known to be by-products of thermoelectric power plant was selected and its applicability for aggregate of concrete mixture was measured. Hardness test, sieve analysis, water-absorption test and SEM analysis were carried out to investigate the possibility of using bottom ash as a replacement of coarse and fine aggregate. Chemical analyses such as ignition loss test and X-ray incidence were carried out also. In addition, values for slump, strength, permeability, freeze and thaw, and carbonation were evaluated in terms of effects of replacement ratio of bottom ash. As the results, it was found that, though bottom ash is in short supply of fine particles and is in lack of cohesion, these problems can be solved by partially mixing with natural aggregates or improving in a process of production. In addition, bottom ash has not only advantage of durability but also acquirement of general compressive strengths in case that a certain proportion of natural aggregate is applied to mixture, in spite that unit water or chemical admixture should be increased to acquire good workability due to plenty of porosity.

• Computers and Concrete
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• v.19 no.6
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• pp.617-623
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• 2017

This work is conducted with the aim of using waste material to reserve the natural resources. The objective is accomplished by conducting experimentation and verify by modeling based on fuzzy logic. In experimentation, concrete is casted by using natural/river sand as fine aggregate and termed as control specimen. Natural sand is conserved by replacing it with used foundry sand (UFS) by an amount of 10, 20 and 30% by weight. Fresh and hardened properties of concrete are investigated at different ages. It is observed that compressive strength and modulus of elasticity reduced with the increase in amount of UFS. Furthermore, concrete compressive strength is predicted by using fuzzy logic model and verified at different replacement ratio and age with experimental observations.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.641-646
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• 2001

Generally, when Fly-Ash was used as replacement material of cement in concrete, it might occur retardation of setting and hardening. So, it is unable to use a large amount of Fly-Ash as replacement for cement. However, if it is used as replacement material of fine aggregate in concrete, we can use a large amount of Fly-Ash and settle a problem of natural-aggregate exhaustion. Furthermore, engineering properties of High Volume Fly-Ash Concrete Is better than that of plain concrete But, the larger Fly-Ash is replaced, the more fluidity of High Volume Fly-Ash Concrete decrease, because porous organization of Fly-Ash adsorb water and Superplasticizer. In this study, after appending additional water to High Volume Fly-Ash Concrete in proportion to weight of Fly-Ash, we intend to find proper ratio which doesn't affect strength and satisfy fluidity As a result of this study, it was found that fluidity of mortar with 25~28 percentage of additional water was satisfied with fluidity of plain mortar, and compressive strength of that was similar to plain mortar's

• Journal of the Korea Institute of Building Construction
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• v.7 no.1 s.23
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• pp.57-62
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• 2007

Generally, the strength of concrete depends on factors of materials, mix proportions, compaction, manufacturing methods and curing and so on. And recently, it has increased the using of crushed sand for concrete due to the exhaustion of good natural aggregate. In case of Korea, in 2004, the using ratio of crushed sand occupies about 28% of whole fine aggregate. This is an experimental study to compare and analyze the influence of W/B ratio and replacement ratio of crushed sand on the fluidity and compressive strength of high strength concrete. For this purpose, the mix proportions of concrete according to the W/B (31.5, 27.5, 23.5%) and replacement ratio of crushed sand (0, 20, 40%) was selected. And then air content, slump-flow, a-lot, compressive strength test were performed.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.443-446
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• 2005

Recently, according to increase use of concrete which is the main material of construction, the natural aggregate of good quality is more and more decreased. Most of all, among the concrete materials, the development of alternation materials of sand is urgently needed. In this study, investigating the production equipment and the sample of crushed sand company and analyzing properties of sand, manufactured mortar by the KS to use crushed sand as the fine aggregate of concrete material. The experiment result is as follows. 1. The density, an absorptivity, and the amount of 0.08mm passage ratio of crushed sand, and the mortar used crushed sand satisfied KS. The mechanical results is similar to sea sand. 2. The crushed sand which used impact crusher instead of cone crusher for 3rd or 4th crusher was similar properties to sea sand, so it is judged that impact crusher has high effect of particle shape improvement of crushed sand.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.1017-1022
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• 2003

The hydraulic structures such as aqueduct tunnels and the drainage canal of the hydroelectric power plant in Japan are almost old. Therefore, the concrete surface of the aqueduct tunnel has received damage by wear-out and the crack, etc. This study was to develop repair mortar mixed a coal ash coarse powder by using two kinds of high early strength cements. As a result, the repair mortar was obtained by substituting the EF cement (maid in Japan) and the MT cement (maid in South Korea) at a rate of 60:40, and substituting the coal ash 30% and the mixing rate 35% of the artificial aggregate for natural fine aggregate.

• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.1
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• pp.21-26
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• 2009

This study was performed to evaluate the physical and mechanical properties of concrete using waste activated carbon. Materials used were ordinary portlant cement, crushed coarse aggregate, natural fine aggregate, waste activated carbon, and superplasticizer. The substitution ratios of waste activated carbon were 0,1,2,3,4,5,6,7,8,9 and 10%. The unit weight was decreased and water absorption ratio was increased with increasing the waste activated carbon content, respectively. When the substitution ratio of waste activated carbon was 3%, compressive strength, flexural strength and dynamic modulus of elastisity were more higher than that of the ordinary portland cement (OPC), and it was decreased with increasing the waste activated carbon content, respectively. The most effective contents of waste activated carbon was 2% in performance and 4% in practical use Accordingly, waste activated carbon can be used for concrete material.